Difficulties can occur here in the crushing of material for grinding which has a high moisture content and has a strong tendency to sticking and/or caking on above a critical moisture value. In the manufacture of cement there are clay-containing raw material components which do not stick or form deposits at a moisture content below 15%, but on the other hand stick severely and even adhere to vertical walls at a moisture content over 18%.
In the case of ore and diamond-containing volcanic rock too the bulk material properties and thus the behaviour of the material for grinding on feeding into the material bed roll mill worsen to a marked extent above a critical moisture content.